Magnetic disk apparatus and method

ABSTRACT

According to one embodiment, a magnetic disk apparatus is provided with a magnetic disk, a buffer memory, and a control circuit. The magnetic disk has plural bands, each of which is a storage area in which data is written by the method of SMR. The control circuit receives a read request from outside. If the data requested to be read is first data of an update target stored in a first band among plural bands, the control circuit reads the first data from the first band, stores the first data in a buffer memory, and updates the first data in the buffer memory. Then, the control circuit transmits the first data in the buffer memory to the outside and writes the first data in the buffer memory to one of the plural bands.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2021-152184, filed on Sep. 17, 2021; theentire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a magnetic diskapparatus and a method.

BACKGROUND

Recently, a technique called Shingled Magnetic Recording (SMR) has beendeveloped as a method to write data to a magnetic disk. According toSMR, when data is to be written to a magnetic disk, the datacorresponding to a subsequent track is written so as to be overlappedwith part of the data corresponding to one already-written track. As aresult, the width of a track (in other words, track pitch) becomesnarrower than the width of a write element, and the recording density ofdata with respect to the magnetic disk is improved.

In SMR, the track pitch is narrower than the write element. Therefore,in order to prevent accidental erase of already written data, write ofnew data is executed sequentially in terms of position with respect tothe magnetic disk. More specifically, in SMR, the magnetic disk isdivided into plural partial areas in a radial direction, and data iswritten to each of the partial areas sequentially in terms of position.The partial areas are also referred to as bands. The write pattern ofcarrying out write sequentially in terms of position is referred to assequential write. The band-unit data stored in each band is referred toas band data.

When part of a band data stored in a band is to be rewritten, the banddata is read from the band and stored in a buffer memory, and rewritewith respect to the band data is executed in the buffer memory. Then,the band data after the rewrite is written to a band.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a configuration of amagnetic disk apparatus according to an embodiment;

FIG. 2 is a diagram for describing a recording surface of each magneticdisk according to the embodiment;

FIG. 3 is a schematic diagram for describing write of an SMR methodexecuted in the magnetic disk apparatus according to the embodiment;

FIG. 4 is a schematic diagram for describing various areas allocated toa first RAM according to the embodiment;

FIG. 5 is a schematic diagram for describing an operation of readingband data which is executed in the magnetic disk apparatus according tothe embodiment;

FIG. 6 is a schematic diagram for describing an operation of updatingdata executed in the magnetic disk apparatus according to theembodiment;

FIG. 7 is a schematic diagram for describing an operation after updatingdata in the magnetic disk apparatus according to the embodiment;

FIG. 8 is a schematic diagram for describing an example of data whichserves as a target of a shared read operation in the magnetic diskapparatus according to the embodiment;

FIG. 9 is a schematic diagram for describing another example of datawhich serves as a target of a shared read operation in the magnetic diskapparatus according to the embodiment;

FIG. 10 is a flow chart illustrating an example of an operation ofsetting a target of an update process executed by the magnetic diskapparatus according to the embodiment;

FIG. 11 is a flow chart illustrating an example of a series ofoperations according to the shared read operation executed by themagnetic disk apparatus according to the embodiment;

FIG. 12 is a schematic diagram for describing an example of operationsof the magnetic disk apparatus according to the embodiment;

FIG. 13 is a schematic diagram for describing an example of operationsin a case in which the magnetic disk apparatus according to theembodiment fails write of the band data; and

FIG. 14 is a schematic diagram for describing an example of operationsof the magnetic disk apparatus according to a modification example theembodiment.

DETAILED DESCRIPTION

According to the present embodiment, the magnetic disk apparatus isprovided with a magnetic disk, a buffer memory, and a control circuit.The magnetic disk has plural bands, each of which is a storage area inwhich data is written by the method of SMR. The control circuit receivesa read request from outside. If the data requested to be read is firstdata of an update target stored in a first band among plural bands, thecontrol circuit reads the first data from the first band, stores thefirst data in a buffer memory, and updates the first data in the buffermemory. Then, the control circuit transmits the first data in the buffermemory to the outside and writes the first data in the buffer memory toone of the plural bands.

Hereinafter, a magnetic disk apparatus a method according to theembodiment will be described in detail with reference to accompanyingdrawings. Note that the present invention is not limited by thisembodiment.

Embodiment

Techniques according to the embodiment can be applied to a magnetic diskapparatus provided with one or more actuator systems. Hereinafter, acase in which the techniques according to the embodiment are applied toa magnetic disk apparatus provided with two actuator systems isdescribed.

FIG. 1 is a diagram illustrating an example of a configuration of amagnetic disk apparatus 1 according to the embodiment. The magnetic diskapparatus 1 is connectable to a host 2. The standards of a communicationpath between the magnetic disk apparatus 1 and the host 2 are notlimited to particular standards. For example, Serial Attached SCSI (SAS)may be employed as the standards of the communication path between themagnetic disk apparatus 1 and the host 2.

The host 2 corresponds to, for example, a processor, a personalcomputer, or a server. The magnetic disk apparatus 1 can receive accesscommands (read commands and write commands) from the host 2.

The magnetic disk apparatus 1 is provided with plural magnetic disks 10.In this case, for example, the magnetic disk apparatus 1 is providedwith two magnetic disks 10 a and 10b. The two magnetic disks 10 areintegrally rotated about a rotation shaft 11 by an unillustrated spindlemotor.

Recording surfaces on which data can be recorded are formed respectivelyon a front surface and a back surface of each of the magnetic disks 10.In other words, the two magnetic disks 10 have four recording surfaces.In order to access each of the four recording surfaces, the magneticdisk apparatus 1 is provided with four magnetic heads HD correspondingto the four recording surfaces.

One pair of first magnetic heads HDa among the four magnetic heads HD isopposed to one pair of recording surfaces of the first magnetic disk 10a. Another pair of second magnetic heads HDb among the four magneticheads HD is opposed to one pair of recording surfaces of the secondmagnetic disks 10 b. Each magnetic head HD executes access, in otherwords, data write and data read with respect to the recording surfaceopposed to the magnetic head. Each magnetic head HD carries out datawrite by using a write element provided in the magnetic head. Eachmagnetic head HD carries out data read by using a read element providedin the magnetic head.

The magnetic disk apparatus 1 is provided with two actuator systems 12,which are individually driven. A first actuator system 12 a among thetwo actuator systems 12 is provided with an actuator arm 13 a and avoice coil motor 14 a. The pair of first magnetic heads HDa is attachedto a distal end of the actuator arm 13 a.

A second actuator system 12 b among the two actuator systems 12 isprovided with an actuator arm 13 b and a voice coil motor 14 b. The pairof second magnetic heads HDb is attached to a distal end of the actuatorarm 13 b.

The two actuator systems 12 can individually rotate about a rotationshaft 15. The rotation shaft 15 is provided at a position parallel tothe rotation shaft 11 and is separated from the rotation shaft 11. Thevoice coil motor 14 a rotates the first actuator system 12 a within apredetermined range about the rotation shaft 15. Accordingly, the pairof first magnetic heads HDa is subjected to relative movement in aradial direction with respect to each recording surface of the firstmagnetic disk 10 a. The voice coil motor 14 b rotates the secondactuator system 12 b within a predetermined range about the rotationshaft 15. Accordingly, the pair of second magnetic heads HDb issubjected to relative movement in a radial direction with respect toeach recording surface of the second magnetic disk 10 b.

Note that the magnetic disk apparatus 1 may be provided with three ormore magnetic disks 10. In such a case, the distal end of the actuatorarm 13 a provided in the first actuator system 12 a is provided withplural first magnetic heads HDa for accessing the recording surfacesprovided on the magnetic disks 10, which are included in the three ormore magnetic disks 10; and the distal end of the actuator arm 13 bprovided in the second actuator system 12 b is provided with pluralsecond magnetic heads HDb for accessing the recording surfaces providedon the other magnetic disks 10, which are included in the three or moremagnetic disks 10.

The magnetic disk apparatus 1 is further provided with a control circuit20. The control circuit 20 communicates with the host 2 via an interfacesuch as a connection pin provided on a chassis (not illustrated) of themagnetic disk apparatus 1 for external connection. The control circuit20 controls each unit of the magnetic disk apparatus 1 in response tocommands, etc. from the host 2. As described above, the commands fromthe host 2 include a write command which requests write and a readcommand which requests read.

The control circuit 20 has a pre-amplifier (Pre Amp) 21 and a Read WriteChannel (RDC) 22 for each actuator system 12. In other words, thecontrol circuit 20 is provided with a pre-amplifier 21 a and a RDC 22 acorresponding to the first actuator system 12 a. Also, the controlcircuit 20 is provided with a pre-amplifier 21 b and a RDC 22 bcorresponding to the second actuator system 12 b.

The control circuit 20 further has a Digital Signal Processor (DSP) 23,a first Random Access Memory (RAM) 24, a Hard Disk Controller (HDC) 25,a Micro Processing Unit 26 (MPU), and a second RAM 27.

The pre-amplifier 21 a amplifies signals, which have been read from therecording surface of the first magnetic disk 10 a by the read element ofeach first magnetic head HDa, and supplies the amplified signals to theRDC 22 a. Also, the pre-amplifier 21 a amplifies signals, which havebeen supplied from the RDC 22 a, and supplies the amplified signals tothe first magnetic head HDa, which is opposed to the recording surfaceserving as a write destination.

The RDC 22 a encodes the data, which is to be written to the firstmagnetic disk 10 a, and supplies the encoded data to the pre-amplifier21 a as signals. Also, the RDC 22 a decodes the signals, which have beenread from the first magnetic disk 10 a and supplied from thepre-amplifier 21 a. The RDC 22 a outputs the decoded signals to the HDC25 as digital data.

The pre-amplifier 21 b amplifies signals, which have been read from thesecond magnetic disk 10 b by the read element of each second magnetichead HDb, and supplies the amplified signals to the RDC 22 b. Also, thepre-amplifier 21 b amplifies signals, which have been supplied from theRDC 22 b, and supplies the amplified signals to the second magnetic headHDb.

The RDC 22 b encodes the data, which is to be written to the secondmagnetic disk 10 b, and supplies the encoded data to the pre-amplifier21 b as signals. Also, the RDC 22 b decodes the signals, which have beenread from the second magnetic disk 10 b and supplied from thepre-amplifier 21 b. The RDC 22 b outputs the decoded signals to the HDC25 as digital data.

The DSP 23 carries out positioning control of each of the magnetic headsHD such as seeking and following by controlling the spindle motor andthe voice coil motor 14.

The first RAM 24 is a buffer memory in which data, etc. transferredbetween the host 2 and the magnetic disks 10 is temporarily stored. Forexample, the data received from the host 2 is written to any of themagnetic disks 10 via the first RAM 24. Also, the data read from the twomagnetic disks 10 is output to the host 2 via the first RAM 24. Detailsof the function of the first RAM 24 as a buffer memory will be describedlater.

The first RAM 24 includes a memory capable of operating at high speed.Also, the first RAM 24 is, for example, a dual port memory capable ofcarrying out plural simultaneous accesses. Note that the first RAM 24may be a single port memory. The first RAM 24 may be built of, forexample, a Dynamic Random Access Memory (DRAM), a Static Random AccessMemory (SRAM), or a combination thereof. Note that the position at whichthe first RAM 24 is provided does not have to be in the control circuit20. The first RAM 24 may be provided outside the control circuit 20.

The HDC 25 executes communication with the host 2. The HDC 25 stores thedata, which has been received from RDCs 22 a and 22 b, in the first RAM24. Then, the HDC 25 transfers the data from the RDCs 22 a and 22 b,which is stored in the first RAM 24, to the host 2.

Also, the HDC 25 stores the data, which has been received from the host2 together with a write command, in the first RAM 24. Then, the HDC 25outputs the data from the host 2, which is stored in the first RAM 24,to the RDCs 22 a and 22 b.

The MPU 26 is a processor, which executes a firmware program. The MPU 26analyzes the commands from the host 2, which have been received by theHDC 25, and carries out monitoring of the state of the magnetic diskapparatus 1, control of each unit of the magnetic disk apparatus 1, etc.

The second RAM 27 functions as, for example, an area in which firmwareand various management information is stored. The second RAM 27 includesa volatile memory, a non-volatile memory, or a combination thereof. Thevolatile memory may be, for example, a SRAM, a DRAM, or a combinationthereof. The non-volatile memory may be, for example, a flash memory.

As described above, the pair of first magnetic heads HDa is provided atthe distal end of the first actuator system 12 a, and the pair of secondmagnetic heads HDb is provided at the distal end of the second actuatorsystem 12 b, which is controlled independently from the first actuatorsystem 12 a. Also, the pre-amplifier 21 and the RDC 22 are provided foreach actuator system 12.

Accordingly, the control circuit 20 can independently control the accessto the first magnetic disk 10 a, which uses the first actuator system 12a and the pair of the first magnetic heads HDa, and the access to thesecond magnetic disk 10 b, which uses the second actuator system 12 band the pair of the second magnetic heads HDb. Therefore, the controlcircuit 20 can execute, in parallel, the access using the first actuatorsystem 12 a and the access using the second actuator system 12 b.

FIG. 2 is a diagram for describing the recording surface of eachmagnetic disk 10 according to the embodiment. The configurations of therecording surfaces of the two magnetic disks 10 are the same. Thisdiagram illustrates one of the front surface and the back surface of acertain magnetic disk 10.

A recording surface 100 is provided on a surface of the magnetic disk10. The recording surface 100 is divided into plural concentric storageareas 110 having a rotation center of the magnetic disk 10 as a centerthereof. In other words, the recording surface 100 is divided into theplural storage areas 110 in the radial direction. The plural storageareas 110 include one media cache area 120 and plural bands 130. Areascalled guard areas in which data write is prohibited are providedbetween the storage areas 110. However, illustration of the guard areasis omitted in this diagram.

In the example illustrated in FIG. 2 , the storage area 110, which isprovided in the outermost side in the radial direction of the recordingsurface 100, corresponds to the media cache area 120. The position ofthe media cache area 120 is not limited to this. The number of the mediacache area(s) 120 provided on the single recording surface 100 is notlimited to one.

Also, the recording surface 100 has four bands 130 as the plural bands130. The number of the bands 130 provided on the recording surface 100is not limited thereto.

Data is written to the bands 130 by the Shingled Magnetic Recording(SMR) method. FIG. 3 is a schematic diagram for describing write of theSMR method executed in the magnetic disk apparatus 1 according to theembodiment.

According to SMR, when data written to each band 130, the datacorresponding to a subsequent track is written so as to be overlappedwith part of the data corresponding to one already-written track.Therefore, as illustrated in FIG. 3 , a track pitch (TP) is narrowerthan a core width (WHw) of the write element of the magnetic head HD. Asa result, the recording density thereof is improved.

Also, in SMR, in order to prevent the writing of the data of new tracksfrom making it difficult to read the data of already-written tracks,write in the band 130 is carried out in either one direction of thedirection from the outer side of the magnetic disk 10 toward theradial-direction inside (in other words, inner side) and the oppositedirection thereof. The direction of write in one band 130 is not changedduring the write.

According to SMR, the track pitch is narrower than the core width WHw ofthe write element. Therefore, when partial data of the data of pluraltracks, which have undergone write sequentially in terms of position bythe SMR method, is to be subjected to rewrite, the data in the trackadjacent to the track including the data of a rewrite target may bedestroyed. In order to prevent such destruction of data, rewrite of datais executed in the unit of the band 130.

For example, in a state in which certain data (described as old data) isstored in a certain band 130, if new data corresponding to the old datais transmitted, the new data is temporarily stored in a storage area(for example, the media cache area 120) which is different from thisband 130. Then, when a predetermined condition is satisfied, all thedata in the band 130 (in other words, band data) is written to the sameor another band 130. In this process, the old data included in the banddata is replaced by new data. The replacement can be also described asupdate. Such a process of reading band data and replacing part of theband data by new data is described as an update process.

The first RAM 24 also functions as a buffer memory for the updateprocess in addition to a buffer memory of data transmitted to/from thehost 2. FIG. 4 is a schematic diagram for describing various areasallocated to the first RAM 24 according to the embodiment. Asillustrated in this diagram, plural areas including a first buffer area241 and a second buffer area 242 are allocated to the first RAM 24.

The first buffer area 241 temporarily stores the data, which has beenread from the magnetic disk 10 in response to a request of read by aread command from the host 2. Note that an operation corresponding to aread command from the host 2 is described as host read. In other words,the first buffer area 241 is used for host read.

The second buffer area 242 temporarily stores band data, which is atarget of an update process.

Herein, techniques compared with the embodiment will be described. Thetechniques compared with the embodiment are described as a comparativeexample. In the comparative example, the control circuit individuallyexecutes the read of band data from a magnetic disk for an updateprocess and the read of data from the magnetic disk for host read.Therefore, even if the same data serves as a target of both the updateprocess and the host read, the control circuit reads the same data twicefrom the magnetic disk. Therefore, efficiency of data read from themagnetic disk is bad.

In the embodiment, in order to improve the efficiency of data read fromthe magnetic disk 10 compared with the comparative example, the controlcircuit 20 executes the read of the band data, which serves as an updatetarget, at the timing when read of part or all of this band data isrequested from the host 2. Hereinafter, the update process according tothe embodiment will be described by using FIG. 5 to FIG. 7 .

FIG. 5 is a schematic diagram for describing an operation of readingband data which is executed in the magnetic disk apparatus 1 accordingto the embodiment.

In the example illustrated in FIG. 5 , it is assumed that, in a state inwhich band data in a certain band 130 a provided on the first magneticdisk 10 a is set as an update target in advance, the host 2 hastransmitted a read command, which requests read of the band data, to themagnetic disk apparatus 1. In such a case, the control circuit 20 readsband data 300 a, which is stored in the band 130 a, by using the firstactuator system 12 a. The control circuit 20 stores the band data 300 a,which has been read from the band 130 a, in both of the first bufferarea 241 and the second buffer area 242. One of the band data 300 storedin the first buffer area 241 and the band data 300 stored in the secondbuffer area 242 is a copy of the other one. In other words, the controlcircuit 20 acquires the two pieces of band data 300 by executing read ofthe band data 300 from the band 130 a once and copying the read banddata 300, and the control circuit 20 stores one of the two pieces ofband data 300 in the first buffer area 241 and stores the other one ofthe two pieces of band data 300 in the second buffer area 242.

At the timing before or after the read of the band data 300 a, thecontrol circuit 20 reads new data 400 b, which is to rewrite the banddata 300 a, from, for example, the media cache area 120 of the magneticdisk 10 and stores the new data in a predetermined storage area (in thiscase, for example, the first RAM 24). If plural pieces of new data torewrite the band data 300 a are present, the control circuit 20 readsall the new data, which is to rewrite the band data 300 a, from themagnetic disk 10 and stores the data in a predetermined storage area.

Note that the data 400 b illustrated in FIG. 5 is new data which is torewrite the band data 300 a. Data 400 a included in the band data 300 ais the part to be rewritten by the data 400 b, in other words, is olddata. In the example illustrated in FIG. 5 , the data 400 a is the onlyold data to be rewritten.

FIG. 6 is a schematic diagram for describing an operation of updatingdata executed in the magnetic disk apparatus 1 according to theembodiment. As illustrated in this diagram, with respect to both theband data 300 a stored in the first buffer area 241 and the band data300 a stored in the second buffer area 242, the control circuit 20replaces the data 400 a by the data 400 b. As a result, each of the banddata 300 a stored in the first buffer area 241 and the band data 300 astored in the second buffer area 242 becomes the band data of a lateststate (band data 300 b illustrated in FIG. 7 ).

FIG. 7 is a schematic diagram for describing an operation after updatingdata in the magnetic disk apparatus 1 according to the embodiment.

The control circuit 20 transmits the band data 300 b, which is in thefirst buffer area 241, to the host 2. Also, the control circuit 20writes the band data 300 b, which is in the second buffer area 242, tothe magnetic disk 10. Herein, for example, the control circuit 20 writesthe band data 300 b to a certain band 130 b of the second magnetic disk10 b by using the second actuator system 12 b.

In this manner, when the band data 300 a serving as a target of theupdate process serves as a target of host read, the control circuit 20reads the band data 300 a only once from the magnetic disk 10 to thefirst RAM 24. Then, the control circuit 20 executes update with respectto the band data 300 a stored in the first RAM 24 and transmits theupdated band data 300 b to the host 2 or writes the updated band data300 b to the magnetic disk 10.

Therefore, according to the embodiment, the number of times of read isreduced compared with the comparative example. In other words, theefficiency of data read from the magnetic disk is improved compared withthe comparative example.

The operation described in FIG. 5 of reading the band data, which is anupdate target and is also a host read target, once from the magneticdisk 10 is described as a shared read operation.

Note that, in the above description, the shared read operation isexecuted in the case in which the band data serving as an update targetserves as a target of host read. The shared read operation can beexecuted also in a case in which part of the band data serving as anupdate target serves as a target of host read.

For example, as illustrated in FIG. 8 , in a state in which band data300 c serves as an update target, data 500 a at a center part of theband data 300 c serves as a target of host read, and data 501 and data502 are not targets of host read. In this case, a shared read operationcan be executed with respect to the band data 300 c. However, the datatransmitted to the host 2 after the shared read operation is the data500 a, and both the data 501 and the data 502 are not transmitted to thehost 2.

Also, for example as illustrated in FIG. 9 , in a state in which bothband data 300 d and band data 300 e serve as update targets, data 500 bacross a boundary of the band data 300 d and the band data 300 e from amiddle of the band data 300 d to a middle of the band data 300 e servesas a target of host read, and the other part (data 503 and data 504 ofFIG. 9 ) does not serve as a target of host read. In this case, theshared read operation can be executed with respect to the band data 300d and the band data 300 e. After the shared read operation, the data 500b is transmitted to the host 2. After the shared read operation, boththe data 503 and the data 504 are not transmitted to the host 2.

FIG. 10 is a flow chart illustrating an example of an operation ofsetting a target of the update process executed by the magnetic diskapparatus 1 according to the embodiment.

The control circuit 20 selects one of one or more bands 130 in whichdata has already been written (S101). Then, the control circuit 20determines whether the band data stored in the selected band 130satisfies the condition(s) to execute the update process or not (S102).

The condition to execute the update process is arbitrarily set. Forexample, a fact that the amount of the old data, which is included inband data and to be rewritten, or the new data, which is to rewrite banddata, exceeds a threshold value can be set as the condition to executethe update process.

In another example, a fact that elapsed time after band data has beenwritten to the magnetic disk 10 exceeds a threshold value can be set asthe condition to execute the update process.

Further, in another example, a fact that the number of times ofoccurrence of errors in read of band data exceeds a threshold value canbe set as the condition to execute the update process.

If the band data stored in the selected band 130 does not satisfy thecondition to execute the update process (S102: No), the control makes atransition to S101, and the control circuit 20 selects another band 130.

If the band data stored in the selected band 130 satisfies the conditionto execute the update process (S102: Yes), the control circuit 20 setsthe band data, which is stored in the selected band, as a target of theupdate process (S103). Then, the control makes a transition to S101, andthe control circuit 20 selects another band 130.

In this manner, the control circuit 20 sequentially selects one or morebands 130 in which data is stored and executes the process of S102 withrespect to the selected band 130, thereby searching for the band datawhich satisfies the condition to execute the update process. The controlcircuit 20 can set all of the one or more band data which satisfies thecondition to execute the update process as the target of the updateprocess by executing the loop process illustrated in FIG. 10 .

Note that the execution interval and execution timing of the loopprocess illustrated in FIG. 10 can be arbitrarily set. The controlcircuit 20 may execute the loop process illustrated in FIG. 10 once ormore at the timing when the process(es) of the command(s) from the host2 is not carried out. The control circuit 20 may execute the loopprocess illustrated in FIG. 10 at a predetermined time interval.

FIG. 11 is a flow chart illustrating an example of a series ofoperations according to the shared read operation executed by themagnetic disk apparatus 1 according to the embodiment.

When a read command is received from the host 2 (S201), the controlcircuit 20 determines whether the data requested to be read by the readcommand belongs to the band data set as the target of the update processor not (S202).

If the data requested to be read belongs to the band data set as thetarget of the update process (S202: Yes), the control circuit 20 readsnew data, which is to rewrite the band data, from the media cache area120 and stores the new data in the first RAM 24 (S203).

Subsequently, the control circuit 20 reads the band data from themagnetic disk 10 and stores the band data in the first RAM 24 (S204).More precisely, the control circuit 20 acquires two pieces of band dataincluding the original band data by copying the band data, which hasbeen read from the magnetic disk 10. Then, the control circuit 20 storesone of the two pieces of band data in the first buffer area 241 andstores the other one of the two pieces of band data in the second bufferarea 242.

The control circuit 20 executes replacement by the new data with respectto each piece of the band data stored in the first RAM 24 (S205). Inother words, the control circuit 20 executes update with respect to eachpiece of the band data stored in the first RAM 24.

Then, the control circuit 20 executes transmission of data to the host 2and write of the band data to the magnetic disk 10 (S206). In S206, thecontrol circuit 20 transmits the data of the part, which is in the banddata in the first buffer area 241 and has been requested to be read, tothe host 2. Also, the control circuit 20 writes the band data in thesecond buffer area 242 to one of the bands 130 in the magnetic disk 10.Then, the series of the operations is completed.

If the data requested to be read does not belong to band data set as atarget of the update process (S202: No), the control circuit 20 readsthe data, which has been requested to be read, from the magnetic disk 10and stores the read data in the first RAM 24 (more specifically, thefirst buffer area 241) (S207). Then, the control circuit 20 transmitsthe data in the first RAM 24 to the host (S208). Then, the series of theoperations is finished.

FIG. 12 is a schematic diagram for describing an example of operationsof the magnetic disk apparatus 1 according to the embodiment. Thisdiagram illustrates data stored in the first buffer area 241, datastored in the second buffer area 242, contents of operations using thefirst actuator system 12 a, and contents of operations using the secondactuator system 12 b. Note that a horizontal axis illustrates theelapsed time based on the point of time of start of host read (in otherwords, the point of time of reception of a read command).

In the example illustrated in FIG. 12 , it is assumed that both banddata BD1 and band data BD2 are the data requested to be read and thatthe band data BD1 and the band data BD2 are recorded in the firstmagnetic disk 10 a.

First, the control circuit 20 reads the band data BD1 from the firstmagnetic disk 10 a by using the first actuator system 12 a (S301). Thecontrol circuit 20 makes two copies of the band data BD1 read from thefirst magnetic disk 10 a, stores one copy of the band data BD1 in thefirst buffer area 241 (S302), and stores the other copy of the band dataBD1 in the second buffer area 242 (S303). The control circuit 20transmits the band data BD1 in the first buffer area 241 to the host 2after carrying out replacement by new data (S304). Also, the controlcircuit 20 writes the band data BD1 in the second buffer area 242 to anarbitrary unused band 130 of the second magnetic disk 10 b by using thesecond actuator system 12 b after carrying out replacement by new data(S305). The control circuit 20 retains the band data BD1 in the secondbuffer area 242 until the write of the band data BD1 to the secondmagnetic disk 10 b is completed.

When the read (S301) of the band data BD1 using the first actuatorsystem 12 a is finished, the control circuit 20 reads the band data BD2from the first magnetic disk 10 a by using the first actuator system 12a (S306). The first actuator system 12 a and the second actuator system12 b can be independently driven. Therefore, the process of S306 isexecuted in parallel to the process of S305. Note that the expression “aprocess N and a process M are executed in parallel to each other” meansthat an execution period of the process N and an execution period of theprocess M are overlapped with each other at least partially.

The control circuit 20 makes two copies of the band data BD2 read fromthe second magnetic disk 10 b, stores one copy of the band data BD2 inthe first buffer area 241 (S307), and stores the other copy of the banddata BD2 in the second buffer area 242 (S308). The control circuit 20transmits the band data BD2 in the first buffer area 241 to the host 2after carrying out replacement by new data (S309). Also, the controlcircuit 20 writes the band data BD2 in the second buffer area 242 to anarbitrary unused band 130 of the second magnetic disk 10 b by using thesecond actuator system 12 b after carrying out replacement by new data(S310). The control circuit 20 retains the band data BD2 in the secondbuffer area 242 until the write of the band data BD2 to the secondmagnetic disk 10 b is completed.

In this manner, in the magnetic disk apparatus 1 according to theembodiment, the control circuit 20 can execute, in parallel to eachother, the write (for example, S305) to the magnetic disk 10 for theupdate process of one piece of band data using one of the actuatorsystems 12 and the shared read operation (for example, S306) of anotherpiece of band data using the other one of the actuator systems 12.

Also, the control circuit 20 can execute, in parallel, the transmissionof certain band data stored in the first RAM 24 to the host 2 (forexample, S304) and the write of the same band data as this band data tothe magnetic disk 10 (for example, S305).

The write of the band data to the magnetic disk 10 fails in some cases.The control circuit 20 checks whether the data can be correctly read ornot by carrying out read of the data of the track, which has undergonenarrowing of the track pitch, every time a predetermined amount of data(for example, data corresponding to one track) is written to themagnetic disk 10. If the data is not correctly read, the write of thedata is assumed to be failure. Note that the patterns of failure of datawrite are not limited thereto. When write of one piece of band data tothe magnetic disk 10 fails, the control circuit 20 retries the write ofthis band data to the magnetic disk 10.

FIG. 13 is a schematic diagram for describing an example of operationsin a case in which the magnetic disk apparatus 1 according to theembodiment fails write of the band data BD1. In this diagram, theoperations same as the operations illustrated in FIG. 12 are denoted bythe same step numbers as FIG. 12 . Also, regarding the operations sameas the operations illustrated in FIG. 12 , descriptions are omitted, ordescriptions are simplified.

First, the control circuit 20 executes the processes of S301 to 304 asin the example illustrated in FIG. 12 . Then, the control circuit 20writes the band data BD1 in the second buffer area 242 to an arbitraryunused band 130 of the second magnetic disk 10 b by using the secondactuator system 12 b after carrying out replacement by new data (S305).

When the write of the band data BD1 to the second magnetic disk 10 bfails in S305, the control circuit 20 retries the write of the band dataBD1 to the second magnetic disk 10 b (S401). In S401, the controlcircuit 20 writes the band data BD1, which has been retained in thesecond buffer area 242 without being erased, to the second magnetic disk10 b. The band 130 of a write destination may be the band 130 used asthe write destination in S305 or may be another arbitrary unused band130. The control circuit 20 retains the band data BD1 in the secondbuffer area 242 until the write of the band data BD1 to the firstmagnetic disk 10 a is completed.

When the read (S301) of the band data BD1 using the first actuatorsystem 12 a is finished, the control circuit 20 reads the band data BD2from the first magnetic disk 10 a by using the first actuator system 12a (S306). The process of S306 can be executed in parallel to the processof S305 or the process of S401.

The control circuit 20 executes the processes of S307 to S309 afterS306. Also, after the process of S401 is completed, the control circuit20 writes the band data BD2, which is in the second buffer area 242, tothe second magnetic disk 10 b by using the second actuator system 12 b(S310). The band data BD2 can be written to an arbitrary unused band130. The control circuit 20 executes the write of the band data BD2after carrying out replacement by new data. The control circuit 20retains the band data BD2 in the second buffer area 242 until the writeof the band data BD2 to the second magnetic disk 10 b is completed.

In this manner, in the magnetic disk apparatus 1 according to theembodiment, the control circuit 20 retains the band data in the secondbuffer area 242 until the write of the band data to the magnetic disk 10is completed. Therefore, even when the write of the band data to themagnetic disk 10 fails, the control circuit 20 can retry the write ofthe band data to the magnetic disk 10.

The band data is retained in the second buffer area 242 until the writeto the magnetic disk 10 is completed. Therefore, when the transmissionof the data to the host 2 is completed, the band data in the firstbuffer area 241 becomes unnecessary. The control circuit 20 disables theband data in the first buffer area 241 which has become unnecessary andcan use the area in the first buffer area 241, in which the band datahas been stored, to store different band data.

Note that, in the above descriptions, in the first RAM 24, the firstbuffer area 241 used for the host read and the second buffer area 242used in the update process are individually provided. One buffer areamay be shared by the host read and the update process. Hereinafter, thetechnique of sharing one buffer area by the host read and the updateprocess will be described as a modification example of the embodiment.

FIG. 14 is a schematic diagram for describing an example of operationsof the magnetic disk apparatus 1 according to a modification example theembodiment. A buffer area in the first RAM 24, which is shared by thehost read and the update process, is described as a third buffer area.This diagram illustrates data stored in the third buffer area, contentsof operations using the first actuator system 12 a, and contents ofoperations using the second actuator system 12 b. Note that, as in FIG.12 and FIG. 13 , a horizontal axis illustrates the elapsed time based onthe point of time of start of host read (in other words, the point oftime of reception of a read command).

Also, in the example illustrated in FIG. 14 , it is assumed that bothband data BD3 and band data BD4 are the data requested to be read andthat the band data BD3 and the band data BD4 are recorded in the firstmagnetic disk 10 a.

First, the control circuit 20 reads the band data BD3 from the firstmagnetic disk 10 a by using the first actuator system 12 a (S501). Thecontrol circuit 20 stores the band data BD3, which has been read fromthe first magnetic disk 10 a, in the third buffer area (S502). Thecontrol circuit 20 transmits the band data BD3 in the third buffer areato the host 2 after carrying out replacement by new data (S503). Also,the control circuit 20 writes the band data BD3, which has undergonereplacement by new data and is in the third buffer area, to an arbitraryunused band 130 of the second magnetic disk 10 b by using the secondactuator system 12 b (S504). The control circuit 20 retains the banddata BD3 in the third buffer area until the write of the band data BD3to the first magnetic disk 10 a is completed.

When the write of the band data BD3 to the second magnetic disk 10 bfails in S504, the control circuit 20 retries the write of the band dataBD3 to the second magnetic disk 10 b (S505). In S505, the controlcircuit 20 writes the band data BD3, which has been retained in thethird buffer area without being erased, to the second magnetic disk 10b. The band 130 of a write destination may be the band 130 used as thewrite destination in S504 or may be another arbitrary unused band 130.

After the read (S501) of the band data BD3 using the first actuatorsystem 12 a is completed, the control circuit 20 reads the band data BD4from the first magnetic disk 10 a by using the first actuator system 12a (S506). The first actuator system 12 a and the second actuator system12 b can be independently driven. Therefore, the process of S506 can beexecuted in parallel to the process of S504 or the process of S505.

The control circuit 20 stores the band data BD4, which has been readfrom the second magnetic disk 10 b, in the third buffer area (S507).Then, the control circuit 20 transmits the band data BD4 in the thirdbuffer area to the host 2 after carrying out replacement by new data(S508). Also, after the write (S505) of the band data BD3 using thesecond actuator system 12 b is completed, the control circuit 20 writesthe band data BD4, which has undergone replacement by new data and is inthe third buffer area, to an arbitrary unused band 130 of the secondmagnetic disk 10 b by using the second actuator system 12 b (S509).

In this manner, to the first RAM 24 as a buffer memory, dedicated areasrespectively for the host read and the update process may be allocated,or one area shared by the host read and the update process may beallocated.

Note that, in the embodiment and the modification example thereof, thecontrol circuit 20 specifies the band 130, which serves as an updatetarget, in advance by the operation described by using FIG. 10 beforethe read command is received from the host 2. The process of specifyingthe band 130, which serves as the update target, may be executed afterthe read command is received. In other words, when the read command isreceived, the control circuit 20 may determine whether the band data towhich the data requested to be read by the read command satisfies thecondition to execute the update process or not.

In the description described above, the magnetic disk apparatus 1provided with the two actuator systems 12 a and 12 b has been describedas an example. The shared read operation according to the embodiment canbe realized as long as the number of the actuator systems provided inthe magnetic disk apparatus is one or more.

More specifically, if the data requested to be read by the host is thedata (described as first data), which is stored in a certain band(described as a first band) among plural bands and has been determinedto be updated, the control circuit reads the first data, which is storedin the first band, by using one of the one or more actuator systems andstores the first data in the buffer memory. The control circuit updatesthe first data in the buffer memory. The control circuit transmits thedata, which is in the first data in the buffer memory and has beenrequested to be read by the host, to the host and writes the first data,which is in the buffer memory, to one of the plural bands by using oneof the one or more actuator systems.

Therefore, compared with a case in which the read of data from themagnetic disk for host read and the read of data from the magnetic diskfor the update process are individually executed, the number of times ofread of data from the magnetic disk is reduced. In other words, theefficiency of the read of data from the magnetic disk can be improved.

If the magnetic disk apparatus is provided with two or more actuatorsystems, the magnetic disk apparatus can further execute, for example,the process of S305 and the process of S306 of FIG. 12 in parallel.

More specifically, if the data requested to be read is the first dataand the data (described as second data), which is stored in another band(described as a second band) among the plural bands and has beendetermined to be updated, the control circuit writes the first data inthe buffer memory to one band among the plural bands by using oneactuator system (described as a third actuator system) among the pluralactuator systems. Then, in parallel to the write of the first data usingthe third actuator system, the control circuit reads the second datafrom the second band by using a fourth actuator system, which isdifferent from the third actuator system among the plural actuatorsystems, and stores the second data in the buffer memory.

Therefore, by utilizing the two actuator systems, as many executionperiods of the update process as possible can be overlapped with theexecution period of the host read. In other words, the magnetic diskapparatus can execute the update process efficiently.

Also, for example as illustrated in FIG. 4 , the magnetic disk apparatuscan be provided with a buffer memory to which the first buffer area forhost read and the second buffer area for the update process of band dataare individually allocated.

In such a case, the control circuit retains the band data in the secondbuffer area until the write of the band data is completed. If the writeof the band data fails, the control circuit retries the write of theband data by using the band data retained in the second buffer area.

Also, in the magnetic disk apparatus according to the embodiment, theband data stored in the buffer memory by the shared read operation istransmitted to the host and is also written to the magnetic disk. Thecontrol circuit can execute, in parallel, the transmission of the banddata, which is stored in the buffer memory, to the host and the write tothe magnetic disk.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A magnetic disk apparatus comprising: a magneticdisk having plural bands, each band serving as a storage area to whichdata is written by a Shingled Magnetic Recording (SMR) method; a buffermemory; and a control circuit configured to receive a request of readfrom outside and, when data requested to be subjected to the read isfirst data of an update target stored in a first band among the pluralbands, read the first data from the first band, stores the first data inthe buffer memory, update the first data in the buffer memory, transmitthe first data in the buffer memory to the outside, and write the firstdata in the buffer memory to one of the plural bands.
 2. The magneticdisk apparatus according to claim 1, further comprising plural actuatorsystems, each actuator system provided with a magnetic head at a distalend, wherein, the control circuit is configured to, when the datarequested to be subjected to the read is the first data and second dataof an update target, the second data being stored in a second banddifferent from the first band among the plural bands, write the firstdata in the buffer memory to one band among the plural bands by using afirst actuator system that is one actuator system among the pluralactuator systems, and, in parallel to the write of the first data usingthe first actuator system, read the second data from the second band byusing a second actuator system that is different from the first actuatorsystem among the plural actuator systems and store the second data inthe buffer memory.
 3. The magnetic disk apparatus according to claim 1,wherein the buffer memory is provided with a first buffer area and asecond buffer area; and the control circuit is configured to copy thefirst data read from the first band to acquire two pieces of the firstdata, store third data serving as one of the two pieces of the firstdata in the first buffer area, store fourth data serving as another oneof the two pieces of the first data in the second buffer area, transmitthe third data in the first buffer area to the outside, and write thefourth data in the second buffer area to one band among the pluralbands.
 4. The magnetic disk apparatus according to claim 2, wherein thebuffer memory is provided with a first buffer area and a second bufferarea; and the control circuit is configured to copy the first data readfrom the first band to acquire two pieces of the first data, store thirddata serving as one of the two pieces of the first data in the firstbuffer area, store fourth data serving as another one of the two piecesof the first data in the second buffer area, transmit the third data inthe first buffer area to the outside, and write the fourth data in thesecond buffer area to one band among the plural bands.
 5. The magneticdisk apparatus according to claim 3, wherein, the control circuit isconfigured to retry the write of the fourth data when the write of thefourth data fails and retain the fourth data in the second buffer areauntil the write of the fourth data is completed.
 6. The magnetic diskapparatus according to claim 4, wherein, the control circuit isconfigured to retry the write of the fourth data when the write of thefourth data fails and retain the fourth data in the second buffer areauntil the write of the fourth data is completed.
 7. A method ofcontrolling a magnetic disk apparatus, the method comprising: receivinga request of read from outside; and, when data requested to be subjectedto the read is first data of an update target stored in a first bandamong plural bands serving as a storage area, each band being possessedby a magnetic disk and to be subjected to write of data by a ShingledMagnetic Recording method, reading the first data from the first band,storing the first data in the buffer memory, updating the first data inthe buffer memory, transmitting the first data in the buffer memory tothe outside, and writing the first data in the buffer memory to one ofthe plural bands.
 8. The method according to claim 7, wherein themagnetic disk apparatus is provided with plural actuator systems, eachactuator system being provided with a magnetic head at a distal end;and, when the data requested to be subjected to the read is the firstdata and second data of an update target, the second data being storedin a second band different from the first band among the plural bands,the method further comprises writing the first data in the buffer memoryto one band among the plural bands by using a first actuator system thatis one actuator system among the plural actuator systems, and, inparallel to the write of the first data using the first actuator system,reading the second data from the second band by using a second actuatorsystem that is different from the first actuator system among the pluralactuator systems and storing the second data in the buffer memory. 9.The method according to claim 7, wherein the buffer memory is providedwith a first buffer area and a second buffer area; and the methodfurther comprises copying the first data read from the first band toacquire two pieces of the first data, storing third data serving as oneof the two pieces of the first data in the first buffer area, storingfourth data serving as another one of the two pieces of the first datain the second buffer area, transmitting the third data in the firstbuffer area to the outside, and writing the fourth data in the secondbuffer area to one band among the plural bands.
 10. The method accordingto claim 8, wherein the buffer memory is provided with a first bufferarea and a second buffer area; and the method further comprises copyingthe first data read from the first band to acquire two pieces of thefirst data, storing third data serving as one of the two pieces of thefirst data in the first buffer area, storing fourth data serving asanother one of the two pieces of the first data in the second bufferarea, transmitting the third data in the first buffer area to theoutside, and writing the fourth data in the second buffer area to oneband among the plural bands.
 11. The method according to claim 9,further comprising: retrying the write of the fourth data when the writeof the fourth data fails, and retaining the fourth data in the secondbuffer area until the write of the fourth data is completed.
 12. Themethod according to claim 10, further comprising: retrying the write ofthe fourth data when the write of the fourth data fails, and retainingthe fourth data in the second buffer area until the write of the fourthdata is completed.